This application claims the benefit of Japanese Patent Applications No.11-322961 filed Nov. 12, 1999 and No.2001-109006 filed Apr. 6, 2001, in the Japanese Patent Office, the disclosures of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to magnetic recording media and magnetic storage apparatuses, and more particularly to a magnetic recording medium and a magnetic storage apparatus which are suited for high-density longitudinal magnetic recording.
2. Description of the Related Art
The recording density of longitudinal magnetic recording media, such as magnetic disks, has been increased considerably, due to the reduction of medium noise and the development of magnetoresistive and high-sensitivity spin-valve heads. A typical longitudinal magnetic recording medium is comprised of a substrate, a seed layer, an underlayer, a magnetic layer where information is written, a C or a Diamond-Like C (DLC) overlayer, and an organic lubricant layer which are successively stacked in this order. For example, the underlayer is made of Cr or a Cr-based alloy, and the magnetic layer is made of a CoCr-based alloy.
The medium noise is reduced by decreasing the exchange coupling between grains, by promoting more Cr segregation in the CoCr-based alloy which forms the magnetic layer. Lowering the medium noise also involves decreasing the grain size and grain size distribution of the magnetic layer, for example, by reducing the thickness of the underlayer. Underlayers which are made of materials such as CrMo, CrTiB, NiAl or the like are presently used in longitudinal magnetic recording media.
The underlayer described above also promotes crystallographic axis (c-axis or magnetic anisotropy axis) orientation in a plane which increases remanence magnetization and thermal stability of bits on the magnetic layer. Much success has been realized with an underlayer having a B2 crystal structure, such as NiAl and FeAl which have the (211) texture when deposited on a glass substrate.
However, the (211) texture is weak for the underlayer having the B2 crystal structure, including NiAl and FeAl. For this reason, it is necessary to increase the thickness of the underlayer in order to improve the (211) texture and to obtain a sufficiently high medium coercivity, as compared to a case where a Cr-based alloy is formed on a NiP layer. As a result, there are limitations in controlling the grain size and the grain size distribution of the magnetic layer by way of reducing the thickness of the underlayer, and that it is difficult to further improve the signal-to-noise ratio (SNR) of the longitudinal magnetic recording medium.
On the other hand, perpendicular magnetic recording media holds promise for high-density recording due to thermal stability of high-density bits. Compared to longitudinal magnetic recording media, the perpendicular magnetic recording media have favorable demagnetizing fields for high linear densities.
A typical perpendicular magnetic recording medium includes a substrate which is usually made of a glass ceramic, a seed layer made of CoCr or Ti, and a magnetic layer made of a Co-based alloy where information is written, an overlayer made of C or Diamond-Like C (DLC), and an organic lubricant layer on the overlayer.
Another typical perpendicular magnetic recording medium has a double magnetic layer structure made up of a soft magnetic layer under the Co-based magnetic layer. The soft magnetic layer is usually made of a NiFe or FeSiAl.
As in the case of the longitudinal magnetic recording medium, the medium noise of the perpendicular magnetic recording medium is reduced by decreasing the exchange coupling between grains, by promoting more Cr segregation in a Co-based alloy which forms the magnetic layer. Lowering the medium noise also involves reducing the grain size and grain size distribution of the magnetic layer, and the proper use of the seed layer which is made of the material such as CoCr and Ti to promote a (0002) growth for the magnetic layer.
However, the conventional perpendicular magnetic recording media do not have a means of controlling or considerably reducing the grain size and grain size distribution of the magnetic layer, and there is a problem in that it is difficult to greatly improve the medium signal-to-noise ratio (SNR).
Accordingly, it is a general object of the present invention to provide a novel and useful magnetic recording medium and magnetic storage apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a magnetic recording medium comprising a substrate, a magnetic layer made of a Co or Co-based alloy, and an underlayer disposed between the substrate and the magnetic layer, where the underlayer is made of an ordered intermetallic material of FCC L12 or FCT L10 crystalline structure, so that c-axis of the magnetic layer is aligned in a predetermined direction. According to the magnetic recording medium of the present invention, it is possible to simultaneously improve the texture of the underlayer and control the grain size and the grain size distribution of the magnetic layer, to thereby enable further improvement of the SNR of the magnetic recording medium. The predetermined direction may be substantially parallel to or substantially perpendicular to an in-plane direction of the magnetic layer, so as to obtain a longitudinal magnetic recording medium or a perpendicular magnetic recording medium.
Still another object of the present invention is to provide a method of producing a magnetic recording medium which includes a base layer, a magnetic layer made of Co or a Co-based alloy, and an underlayer disposed between the base layer and the magnetic layer, comprising the step of depositing the underlayer which is made of a (111)-textured ordered intermetallic material of FCC L12 crystalline structure or FCT L10 crystalline structure on the base layer which is made of glass or oxidized NiP, at a deposition temperature of approximately 140 to approximately 180xc2x0 C. According to the method of producing the magnetic recording medium of the present invention, it is possible to simultaneously improve the texture of the underlayer and control the grain size and the grain size distribution of the magnetic layer, to thereby enable further improvement of the SNR of the magnetic recording medium.
A further object of the present invention is to provide a magnetic storage apparatus comprising a head, and at least one magnetic recording medium which includes a substrate, a magnetic layer made of Co or a Co-based alloy, and an underlayer disposed between the substrate and the magnetic layer, where the underlayer is made of an ordered intermetallic material of FCC L12 crystalline structure or FCT L10 crystalline structure on the substrate, so that c-axis of the magnetic layer is aligned in a predetermined direction. According to the magnetic storage apparatus of the present invention, it is possible to simultaneously improve the texture of the underlayer and control the grain size and the grain size distribution of the magnetic layer, to thereby enable further improvement of the SNR of the magnetic recording medium, so that a high-quality high-density recording and reproduction can be achieved. In addition, the predetermined direction may be substantially parallel to or substantially perpendicular to an in-plane direction of the magnetic layer, so as to realize a longitudinal magnetic recording and reproduction or a perpendicular magnetic recording and reproduction.